U.S. patent number 7,338,403 [Application Number 10/930,033] was granted by the patent office on 2008-03-04 for torque coupling with power-operated clutch actuator.
This patent grant is currently assigned to Magna Powertrain USA, Inc.. Invention is credited to Dumitru Puiu.
United States Patent |
7,338,403 |
Puiu |
March 4, 2008 |
Torque coupling with power-operated clutch actuator
Abstract
A torque transfer mechanism and a control system are disclosed
for adaptively controlling the transfer of drive torque between
first and second rotary members in a power transmission device of
the type used in motor vehicle driveline applications. The torque
transfer mechanism includes a main clutch assembly operably
disposed between the first and second rotary members, a pilot
clutch assembly and a clutch operator assembly. The clutch operator
assembly includes a rotary cam driven by an electric motor and a
pivotal mode fork.
Inventors: |
Puiu; Dumitru (Sterling
Heights, MI) |
Assignee: |
Magna Powertrain USA, Inc.
(Troy, MI)
|
Family
ID: |
35944170 |
Appl.
No.: |
10/930,033 |
Filed: |
August 30, 2004 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060046888 A1 |
Mar 2, 2006 |
|
Current U.S.
Class: |
475/223;
192/35 |
Current CPC
Class: |
B60K
17/16 (20130101); B60K 17/35 (20130101); F16H
48/05 (20130101); F16H 48/08 (20130101); F16H
48/10 (20130101); F16H 48/11 (20130101); F16H
48/19 (20130101); F16H 48/22 (20130101); F16H
48/295 (20130101); F16H 48/30 (20130101); F16H
48/34 (20130101); B60K 23/04 (20130101); B60K
23/0808 (20130101); F16H 48/12 (20130101); F16H
2048/106 (20130101); F16H 2048/204 (20130101); F16H
2048/343 (20130101) |
Current International
Class: |
F16H
48/20 (20060101); F16D 13/04 (20060101) |
Field of
Search: |
;192/84.6,84.7,35,93A,99A,83R,99S ;180/247,223 ;475/210-213,223,225
;74/665F,665G |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
3908478 |
|
May 1989 |
|
DE |
|
62-18117 |
|
Jan 1990 |
|
JP |
|
63-66927 |
|
Mar 1990 |
|
JP |
|
Primary Examiner: Pang; Roger
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Claims
What is claimed is:
1. A power transmission device comprising: a rotary input member
adapted to receive drive torque from a source of drive torque; a
rotary output member adapted to transmit drive torque to an output
device; a main clutch operably disposed between said input and
output members; a ballramp unit having a first cam member
engageable with said main clutch, a second cam member, and rollers
disposed between said first and second cam members; a pilot clutch
operably disposed between said input member and said second cam
member; a clutch operator assembly including a mode fork having a
first segment engageable with said pilot clutch and a second
segment engaging a cam surface on a rotary cam; an electric motor
for driving said rotary cam such that rotation of said rotary cam
in a first direction causes pivotal movement of said mode fork into
engagement with said pilot clutch while rotation of said rotary cam
in a second direction causes pivotal movement of said mode fork to
disengage said pilot clutch; and a control system for adaptively
controlling actuation of said electric motor.
2. The power transmission device of claim 1 wherein said first cam
member of said ballramp unit is axially moveable between first and
second positions for applying corresponding minimum and maximum
clutch engagement forces to said main clutch, and wherein said
first cam member is axially moveable in response to angular
movement of said second cam member relative to said first cam
member that is caused by a pilot activation force applied by said
mode fork to said pilot clutch.
3. The power transmission device of claim 2 wherein said mode fork
is operable in a first position to apply a minimum pilot activation
force to said pilot clutch so as to permit said first cam member to
move to its first position, and wherein said mode fork is operable
in a second position to apply a maximum pilot activation force to
said pilot clutch so as to permit said first cam member to move to
its second position.
4. The power transmission of claim 3 wherein said rotary cam
includes a hub segment driven by said electric motor along a motor
axis of rotation and an upstanding cam segment defining said cam
surface thereon, wherein said second segment of said mode fork
includes a follower that engages said cam surface on said cam
segment, and wherein the profile of said cam surface on said cam
segment is configured to move the follower substantially parallel
to said motor axis of rotation to cause pivotal movement of said
mode fork toward its second position in response to rotation of
said rotary cam by said motor in said first rotary direction and
also cause pivotal movement of said mode fork toward its first
position in response to rotation of said rotary cam in said second
rotary direction.
5. The power transmission device of claim 4 wherein said main
clutch includes a first clutch member driven by said input member,
a second clutch member driving said output member, and a main
clutch pack operably disposed between said first and second clutch
members, wherein said pilot clutch includes a pilot clutch pack
operably disposed between said second cam member of said ballramp
unit and said first clutch member, and a pressure plate engageable
with said pilot clutch pack, and wherein an axially moveable thrust
member is disposed between said pressure plate and said first
segment of said mode fork.
6. The power transmission device of claim 1 wherein said input
member is a first shaft in a transfer case and said output member
is a second shaft of said transfer case.
7. The power transmission device of claim 1 wherein said input
member is driven by a powertrain of a motor vehicle and said output
member is connected to a differential unit of a drive axle
assembly.
8. The power transmission device of claim 1 defining a drive axle
assembly having a differential unit interconnecting a pair of
axleshafts, and wherein said input member is a differential carrier
of said differential unit, said output member is one of said
axleshafts, and said main clutch is arranged to adaptively limit
slip between said axleshafts.
9. The power transmission of claim 1 wherein said control system is
operable to control the position of said rotary cam to cause said
main clutch to transfer a desired magnitude of torque.
10. The power transmission of claim 1 further including an encoder
operable to output a signal indicative of the rotary position of
said rotary cam to said control system, said rotary position being
indicative of the magnitude of torque transferred by said main
clutch.
11. A transfer case comprising: a first shaft; a second shaft; a
main clutch assembly having a hub coupled for rotation with said
first shaft, a drum coupled for rotation with said second shaft, a
main clutch pacK having inner clutch plates coupled for rotation
with said hub and outer clutch plates coupled for rotation with
said drum, and a ballramp unit having a first cam member operable
to exert a clutch engagement force on said main clutch pack in
response to angular movement of a second cam member; a pilot clutch
assembly having a pilot clutch pack with inner clutch plates
coupled for rotation with said hub and outer clutch plates coupled
for rotation with said second cam member, and a thrust member
operable to exert a pilot clutch activation force on said pilot
clutch pack; a clutch operator assembly including a mode fork
having a first segment engageable with said thrust member and a
second segment engageable with a cam surface on a rotary cam; an
electric motor for driving said rotary cam so as to control pivotal
movement of said mode fork and the magnitude of said pilot clutch
activation force exerted by said thrust member on said pilot clutch
pack; and a control system for controlling actuation of said
electric motor.
12. The transfer case of claim 11 wherein said first cam member of
said ballramp unit is axially moveable between first and second
positions for applying corresponding minimum and maximum clutch
engagement forces to said main clutch pack, and wherein said first
cam member is axially moveable in response to angular movement of
said second cam member relative to said first cam member caused by
said pilot activation force applied by said pilot clutch pack.
13. The transfer case of claim 12 wherein said mode fork is
operable in a first position to apply a minimum pilot activation
force to said pilot clutch pack so as to permit said first cam
member to be located in its first position, and wherein said mode
fork is operable in a second position to apply a maximum pilot
activation force to said pilot clutch so as to cause said first cam
member to move to its second position.
14. The transfer case of claim 13 wherein said rotary cam includes
a hub segment driven by said electric motor and an upstanding cam
segment defining said cam surface thereon, wherein said second
segment of said mode fork includes a follower that engages said cam
surface on said cam segment, and wherein the profile of said cam
surface on said cam segment is configured to cause pivotal movement
of said mode fork toward its second position in response to
rotation of said rotary cam by said motor in a first rotary
direction and cause pivotal movement of said mode fork toward its
first position in response to rotation of said rotary cam in a
second rotary direction.
Description
FIELD OF THE INVENTION
The present invention relates generally to power transfer systems
for controlling the distribution of drive torque between the front
and rear drivelines of a four-wheel drive vehicle and/or the left
and right wheels of an axle assembly. More particularly, the
present invention is directed to a power transmission device for
use in motor vehicle driveline applications having a torque
transfer mechanism equipped with a power-operated clutch actuator
that is operable for controlling actuation of a multi-plate
friction clutch.
BACKGROUND OF THE INVENTION
In view of increased demand for four-wheel drive vehicles, a
plethora of power transfer systems are currently being incorporated
into vehicular driveline applications for transferring drive torque
to the wheels. In many vehicles, a power transmission device is
operably installed between the primary and secondary drivelines.
Such power transmission devices are typically equipped with a
torque transfer mechanism for selectively and/or automatically
transferring drive torque from the primary driveline to the
secondary driveline to establish a four-wheel drive mode of
operation. For example, the torque transfer mechanism can include a
dog-type lock-up clutch that can be selectively engaged for rigidly
coupling the secondary driveline to the primary driveline to
establish a "part-time" four-wheel drive mode. When the lock-up
clutch is released, drive torque is only delivered to the primary
driveline for establishing a two-wheel drive mode.
A modern trend in four-wheel drive motor vehicles is to equip the
power transmission device with an adaptively controlled transfer
clutch in place of the lock-up clutch. The transfer clutch is
operable for automatically directing drive torque to the secondary
wheels, without any input or action on the part of the vehicle
operator, when traction is lost at the primary wheels for
establishing an "on-demand" four-wheel drive mode. Typically, the
transfer clutch includes a multi-plate clutch assembly that is
installed between the primary and secondary drivelines and a clutch
actuator for generating a clutch engagement force that is applied
to the clutch assembly. The clutch actuator can be a power-operated
device that is actuated in response to electric control signals
sent from an electronic controller unit (ECU). The electric control
signals are typically based on changes in current operating
characteristics of the vehicle (i.e., vehicle speed, interaxle
speed difference, acceleration, steering angle, etc.; ) as detected
by various sensors. Thus, such "on-demand" transfer clutch can
utilize adaptive control schemes for automatically controlling
torque distribution during all types of driving and road
conditions. Such adaptively controlled transfer clutches can also
be used in association with a center differential operably
installed between the primary and secondary drivelines for
automatically controlling interaxle slip and torque biasing in a
full-time four-wheel drive application.
A large number of adaptively controlled transfer clutches have been
developed with an electro-mechanical clutch actuator that can
regulate the amount of drive torque transferred to the secondary
driveline as a function of the electric control signal applied
thereto. In some applications, the transfer clutch employs an
electromagnetic clutch as the power-operated clutch actuator. For
example, U.S. Pat. No. 5,407,024 discloses a electromagnetic coil
that is incrementally activated to control movement of a ball-ramp
drive assembly for applying a clutch engagement force to the
multi-plate clutch assembly. Likewise, Japanese Laid-open Patent
Application No. 62-18117 discloses a transfer clutch equipped with
an electromagnetic clutch actuator for directly controlling
actuation of the multi-plate clutch pack assembly. Also, U.S. Pat.
No. 6,158,561 discloses use of an electromagnetic actuator for
engaging a pilot clutch which, in turn, controls energization of a
ballramp unit for engaging the main clutch.
As an alternative to such electromagnetic clutch actuation systems,
the transfer clutch can employ an electric motor and a mechanical
drive assembly as the power-operated clutch actuator. For example,
U.S. Pat. No. 5,323,871 discloses a transfer clutch equipped with
an electric motor that controls rotation of a sector plate which,
in turn, controls pivotal movement of a lever arm that is operable
for applying the clutch engagement force to the multi-plate clutch
assembly. Likewise, Japanese Laid-open Patent Application No.
63-66927 discloses a transfer clutch which uses an electric motor
to rotate one cam plate of a ball-ramp operator for engaging the
multi-plate clutch assembly. Finally, U.S. Pat. Nos. 4,895,236 and
5,423,235 respectively disclose a transfer clutch having an
electric motor which drives a reduction gearset for controlling
movement of a ball screw operator and a ball-ramp operator which,
in turn, apply the clutch engagement force to the clutch
assembly.
In contrast to the electro-mechanical clutch actuators discussed
above, it is also well known to equip the transfer clutch with an
electro-hydraulic clutch actuator. For example, U.S. Pat. Nos.
4,862,769 and 5,224,906 generally disclose use of an electric motor
or solenoid to control the fluid pressure exerted by an apply
piston on a multi-plate clutch assembly. In addition, U.S. Pat. No.
6,520,880 discloses a hydraulic actuation system for controlling
the fluid pressure supplied to a hydraulic motor arranged which is
associated with a differential gear mechanism in a drive axle
assembly.
While many adaptive clutch actuation systems similar to those
described above are currently used in four-wheel drive vehicles, a
need exists to advance the technology and address recognized system
limitations. For example, the size and weight of the friction
clutch components and the electrical power requirements of the
clutch actuator needed to provide the large clutch engagement loads
make many systems cost prohibitive for use in most four-wheel drive
vehicle applications. In an effort to address these concerns, new
technologies are being developed for use in power-operated clutch
actuator applications.
SUMMARY OF THE INVENTION
Thus, its is an objective of the present invention to provide a
power transmission device for use in a motor vehicle having a
torque transfer mechanism equipped with a unique power-operated
clutch actuator that is operable to control engagement of a
multi-plate clutch assembly.
As a related objective of the present invention, the torque
transfer mechanism is well-suited for use in motor vehicle
driveline applications to control the transfer of drive torque
between first and second rotary members.
According to each preferred embodiment of the present invention, a
torque transfer mechanism and a control system are disclosed for
adaptively controlling the transfer of drive torque between first
and second rotary members in a power transmission device of the
type used in motor vehicle driveline applications. The torque
transfer mechanism includes a main clutch assembly operably
disposed between the first and second rotary members, a pilot
clutch assembly and a clutch operator assembly. The clutch operator
assembly includes a rotary cam and a pivotal mode fork. During
operation, the control system functions to control the amount and
direction of angular movement of the rotary cam. Such angular
movement of the rotary cam causes corresponding pivotal movement of
the mode fork for actuating the pilot clutch assembly. Such
actuation of the pilot clutch assembly functions to control the
magnitude of a compressive clutch engagement force that is applied
to the main clutch assembly, thereby controlling the drive torque
transferred from the first rotary member to the second rotary
member.
According to another feature of the present invention, the control
system includes an electric motor for driving the rotary cam,
vehicle sensors for detecting various operating characteristics of
the motor vehicle and an electronic control unit (ECU) for
receiving input signals from the vehicle sensors and controlling
energization of the electric motor.
The torque transfer mechanism of the present invention is adapted
for use in a power transmission device for adaptively controlling
the drive torque transferred between a primary driveline and a
secondary driveline. According to one preferred application, the
power transmission device of the present invention is a transfer
case with the torque transfer mechanism arranged as a torque
transfer coupling for providing on-demand torque transfer from the
primary driveline to the secondary driveline. In a related
application, the torque transfer mechanism is arranged as a torque
bias coupling for varying the torque distribution and limiting
interaxle slip between the primary and secondary driveline.
According to another preferred application, the power transmission
device is a drive axle assembly with the torque transfer mechanism
arranged as a torque bias coupling to control speed differentiation
and torque distribution across a differential unit.
BRIEF DESCRIPTION OF THE DRAWINGS
Further objects, features and advantages of the present invention
will become apparent to those skilled in the art from analysis of
the following written description, the appended claims, and
accompanying drawings in which:
FIG. 1 illustrates the drivetrain of a four-wheel drive vehicle
equipped with a power transmission device according to the present
invention;
FIG. 2 is a sectional view of a transfer case associated with the
drivetrain shown in FIG. 1 and which is equipped with a torque
transfer mechanism according to a preferred embodiment of the
present invention;
FIGS. 3 and 4 are enlarged partial views taken from FIG. 2 showing
components of the torque transfer mechanism is greater detail;
FIG. 5 is a schematic illustration of an alternative driveline for
a four-wheel drive motor vehicle equipped with a power transmission
device of the present invention;
FIG. 6 is a schematic illustration of a drive axle assembly
associated with the drivetrain shown in FIG. 5 and equipped with a
torque transfer mechanism according to the present invention;
FIG. 7 is a schematic illustration of an alternative drive axle
assembly operable for use with either of the drivetrain shown in
FIGS. 1 and 5;
FIG. 8 is a schematic illustration of another alternative
embodiment of a power transmission device according to the present
invention;
FIG. 9 illustrates another alternative drivetrain arrangement for a
four-wheel drive motor vehicle equipped with another power
transmission device embodying the present invention;
FIGS. 10 through 13 schematically illustrate different embodiments
of the power transmission device shown in FIG. 9; and
FIG. 14 is a schematic illustration of an alternative construction
for the power transmission device shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to a torque transfer mechanism
that can be adaptively controlled for modulating the torque
transferred from a first rotary member to a second rotary member.
The torque transfer mechanism finds particular application in power
transmission devices for use in motor vehicle drivelines such as,
for example, a torque transfer clutch in a transfer case, a power
take-off unit or an in-line torque coupling, a torque biasing
clutch associated with a differential unit in full-time transfer
cases or power take-off units or in a drive axle assembly, or any
other possible torque transfer application. Thus, while the present
invention is hereinafter described in association with particular
power transmission devices for use in specific driveline
applications, it will be understood that the arrangements shown and
described are merely intended to illustrate embodiments of the
present invention.
With particular reference to FIG. 1 of the drawings, a drivetrain
10 for a four-wheel drive vehicle is shown. Drivetrain 10 includes
a primary driveline 12, a secondary driveline 14, and a powertrain
16 for delivering rotary tractive power (i.e., drive torque) to the
drivelines. In the particular arrangement shown, primary driveline
12 is the rear driveline while secondary driveline 14 is the front
driveline. Powertrain 16 includes an engine 18, a multi-speed
transmission 20, and a power transmission device hereinafter
referred to as transfer case 22. Rear driveline 12 includes a pair
of rear wheels 24 connected at opposite ends of a rear axle
assembly 26 having a rear differential 28 coupled to one end of a
rear prop shaft 30, the opposite end of which is coupled to a rear
output shaft 32 of transfer case 22. Likewise, front driveline 14
includes a pair of front wheels 34 connected at opposite ends of a
front axle assembly 36 having a front differential 38 coupled to
one end of a front prop shaft 40, the opposite end of which is
coupled to a front prop shaft 42 of transfer case 22.
With continued reference to the drawings, drivetrain 10 is shown to
further include an electronically-controlled power transfer system
44 for permitting a vehicle operator to select between a two-wheel
drive mode, a locked ("part-time") four-wheel drive mode, and an
adaptive ("on-demand") four-wheel drive mode. In this regard,
transfer case 22 is equipped with a transfer clutch 50 that can be
selectively actuated for transferring drive torque from rear output
shaft 32 to front output shaft 42 for establishing both of the
part-time and on-demand four-wheel drive modes. Power transfer
system 44 further includes an electromechanical clutch actuator 52
for actuating transfer clutch 50, vehicle sensors 54 for detecting
certain dynamic and operational characteristics of the motor
vehicle, a mode select mechanism 56 for permitting the vehicle
operator to select one of the available drive modes, and an
electronic control unit (ECU) 58 for controlling actuation of
clutch actuator 52 in response to input signals from vehicle
sensors 54 and mode selector 56.
Transfer case 22 is shown in FIG. 2 to include a multi-piece
housing 60 from which rear output shaft 32 is rotatably supported
by a pair of laterally-spaced bearing assemblies 62. Rear output
shaft 32 includes an internally-splined first end segment 64
adapted for connection to the output shaft of transmission 20 and a
yoke assembly 66 secured to its second end segment 68 that is
adapted for connection to rear propshaft 30. Front output shaft 42
is likewise rotatably supported from housing 60 by a pair of
laterally-spaced bearing assemblies 70 and includes a yoke-type end
segment 72 that is adapted for connection to front propshaft
40.
In general, transfer clutch 50 and electromechanical clutch
actuator 52 define a torque transfer mechanism according to the
preferred embodiment of the present invention. Transfer clutch 50
includes a main clutch assembly 74 and a pilot clutch assembly 76.
Main clutch assembly 74 is shown to include a multi-plate friction
clutch 78 and a ballramp unit 80. Likewise, pilot clutch assembly
76 is shown to include a multi-plate friction clutch 82 and a
thrust bearing unit 84. Friction clutch 78 includes a hub 86 fixed
(i.e., splined) for rotation with rear output shaft 32, a drum 88
and a multi-plate clutch pack 90 that is operably disposed between
hub 84 and drum 88. Clutch pack 90 includes a set of outer clutch
plates 92 splined for rotation with drum 88 and which are
interleaved with a set of inner clutch plates 94 splined for
rotation with hub 84. As will be detailed, clutch actuator 52 is
operable for causing a compressive clutch engagement force to be
exerted on clutch pack 90. Such engagement of clutch pack 90 causes
rotary power ("drive torque") to be transferred from rear output
shaft 32 to front output shaft 42 through a transfer assembly 96.
Transfer assembly 96 includes a first sprocket 98 fixed (i.e.,
splined) for rotation with drum 88, a second sprocket 100 fixed
(i.e., splined) for rotation with front output shaft 42, and a
power chain 102 encircling sprockets 98 and 100. First sprocket 98
is shown splined to an end plate segment 104 of drum 88 and is
rotatably supported on rear output shaft 32 via a suitable bearing
assembly 106. A thrust bearing 108 is shown disposed between first
sprocket 102 and a lock ring 109 fixed to rear output shaft 32.
Ballramp unit 80 includes a first cam member 110, a second cam
member 112, and rollers 114. First cam member 110 is splined for
common rotation with drum 88 and bi-directional translational
movement relative to clutch pack 90. Specifically, first cam member
110 is axially moveable between a first or "released" position and
a second or "locked" position. In its released position, first cam
member exerts a minimum clutch engagement force on clutch pack 90
such that virtually no drive torque is transferred from rear output
shaft 32 to front output shaft 42, thereby establishing the
two-wheel drive mode. In contrast, movement of first cam member 110
to its locked position causes a maximum clutch engagement force to
be exerted on clutch pack 90 such that front output shaft 42 is, in
effect, coupled for common rotation with rear output shaft 32,
thereby establishing the part-time four-wheel drive mode.
Accordingly, variable control of the movement of first cam member
110 between its released and locked position results in adaptive
regulation of the drive torque transferred to front output shaft
42, thereby establishing the on-demand four-wheel drive mode.
Second cam member 112 of ballramp unit 80 is operably connected to
second friction clutch 82. In addition, rollers 114 are disposed in
cam channels defined between first cam tracks 116 formed in first
cam member 110 and second cam tracks 118 formed in second cam
member 112. Preferably, a plurality of such cam channels are
provided which are each configured as an oblique section of a
helical torus. Balls 114 and cam tracks 116,118 may be replaced
with alternative components and/or tapered ramp profiles that
functions to cause axial movement of first cam member 110 in
response to relative angular movement between the cam members. In
any arrangement, the load transferring components can not be
self-locking or self-engaging so as to permit fine control over the
translational movement of first cam member 110 for providing
precise control of the clutch engagement force applied to clutch
pack 90. A thrust bearing assembly 120 is disposed between second
cam member 112 and a retainer plate 122 that is splined to drum 88.
A lock ring 124 axially locates retainer plate 122 for preventing
axial movement of second cam member 112.
Second friction clutch 82 includes a multi-plate clutch pack 128
that is operably disposed between second cam member 112 of ballramp
unit 80 and hub 86 of first friction clutch 78. Clutch pack 128
includes a set of outer plates 130 splined for rotation with second
cam member 112 and which are interleaved with a set of inner clutch
plates 132 splined for rotation with hub 86. Thrust bearing unit 84
includes a first thrust ring 134, a second thrust ring 136 and
rollers 138. First thrust ring 134 is fixed to a pressure plate 140
which, in turn, is splined for rotation with hub 86 of first
friction clutch 78. Rollers 138 are disposed in roller channels
defined between first thrust ring 136 and second thrust ring 136.
Bi-directional axial movement of thrust bearing unit 84 permits
accurate control of bi-directional translational movement of
pressure plate 140 relative to clutch pack 128. Such translational
movement of pressure plate 140 is operable for controlling the
magnitude of pilot actuation force exerted on clutch pack 128
which, in turn, controls energization of ballramp unit 80. With
pressure plate 140 in a first or "retracted" position, a minimum
pilot actuation force is exerted on clutch pack 128 such that first
and second cam members of ballramp unit 80 are permitted to rotate
together, thereby maintaining first cam member 110 in its released
position. In contrast, movement of pressure plate 140 to a second
or "extended" position causes a maximum pilot actuation force to be
exerted on clutch pack 128 which, in turn, causes second cam member
112 to rotate relative to first cam member 110. Such relative
rotation results in axial movement of first cam member 110 to its
locked position.
Ballramp unit 80 further includes a torsional return spring (not
shown) that is operably connected between first cam member 110 and
second cam member 112. The return spring functions to angularly
bias the cam members for moving first cam member 110 toward its
released position so as to de-energize ballramp unit 80. Such
angular movement between the cam members due to the biasing of the
return spring also results in rearward translation of first thrust
ring 134 toward its retracted position for de-energizing pilot
clutch 82.
To provide means for moving pressure plate 140 between its
retracted and extended positions, clutch actuator 52 generally
includes a clutch operator assembly 152 and an electric power unit
154. Power unit 154 is secured to housing 60 and includes an
electric motor 156 and a rotary position sensor, such as an encoder
158. Clutch operator assembly 152 is shown to include a rotary
drive mechanism 160 and a pivotal mode fork 162. Drive mechanism
160 includes a drive shaft 164 having a first end segment 166 fixed
via a spline connection 168 for rotation with a rotary output shaft
170 of electric motor 156. As seen, first end segment 166 is
rotatably supported by a bearing assembly 171 while a second end
segment 172 of drive shaft 164 is rotatably supported in a guide
sleeve 174 which, in turn, is fixed via a lock nut 176 to a portion
of housing 60. A rotary cam 178 has a tubular hub segment 180 fixed
via a spline connection 182 for rotation with drive shaft 164 and
is axially restrained thereon via engagement at one end with a
shoulder segment 184 and at its opposite end via lock ring 186. In
addition, rotary cam 178 further includes an upstanding cam segment
188 that defines a cam surface 190.
As best seen from FIGS. 3 and 4, mode fork 162 is shown to include
a hub segment 192, a fork segment 194 and a lever segment 196. Hub
segment 192 is journalled on a pivot shaft 198 secured to housing
60 so as to permit pivotal movement of fork segment 194 relative to
pilot clutch assembly 82 and pivotal movement of lever segment 196
relative to rotary cam 178. Fork segment 194 has a pair of tang
members 200 that are laterally offset to surround rear output shaft
32. Each tang member 200 includes at least two lugs 202 that are
maintained in engagement with second thrust ring 136. In addition,
a roller assembly 204 is mounted to a terminal end 206 of lever
segment 196 and is maintained in rolling engagement with cam
surface 190 on cam segment 188 of rotary cam 178.
In operation, actuation of motor 156 causes rotary cam 178 to
rotate in a first direction which, in turn, results in
corresponding pivotal movement of mode fork 162 for moving thrust
bearing unit 84 from its retracted position toward its extended
position. Accordingly, the resultant amount of forward axial
movement of first thrust ring 134 causes pressure plate 140 to
exert a corresponding pilot actuation force on clutch pack 128.
Engagement of clutch pack 128 effectively couples second cam member
112 of ballramp unit 80 for rotation with hub 86 and rear output
shaft 32. This action results it relative rotation between cam
members 110 and 112 and which, in turn, results in translational
movement of first cam member 110 toward its locked position.
With pressure plate 140 in its retracted position, first cam member
110 is located in its released position such that virtually no
drive torque is transferred from rear output shaft 32 to front
output shaft 42 through transfer clutch 50, thereby effectively
establishing the two-wheel drive mode. In contrast, movement of
pressure plate 140 to its extended position causes corresponding
movement of cam member 110 to its locked position. As such, a
maximum amount of drive torque is transferred to front output shaft
42 for, in effect, coupling front output shaft 42 for common
rotation with rear output shaft 32, thereby establishing the
part-time four-wheel drive mode. Accordingly, controlling the
position of pressure plate 140 between its retracted and extended
positions relative to clutch pack 128 permits variable control of
the amount of drive torque transferred from rear output shaft 32 to
front output shaft 42, thereby establishing the on-demand
four-wheel drive mode. Thus, the control signals supplied to
electric motor 156 control the angular position of rotary cam 178
for controlling the pivoted position of mode fork 162 and, in turn,
the axial movement of pressure plate 140 between its retracted and
extended positions.
ECU 58 sends electrical control signals to electric motor 156 for
accurately controlling the rotated position of rotary cam 178 by
utilizing a predefined control strategy that is based on the mode
signal from mode selector 56 and the sensor input signals from
vehicle sensors 54. Encoder 158 sends a signal to ECU 58 that is
indicative of the rotated position of rotary cam 178. In operation,
if the two-wheel drive mode is selected, motor 156 drives rotary
cam 178 in its second direction until pressure plate 140 is
permitted to return to its retracted position. With pilot clutch 82
released, ballramp unit 80 is de-energized such that main clutch 78
is also released. In contrast, upon selection of the part-time
four-wheel drive mode, motor 156 drives rotary cam 178 until
pressure plate 140 is located in its extended position for fully
engaging pilot clutch 82. As such, ballramp unit 80 is energized to
move first cam member 110 to its locked position for fully engaging
main friction clutch 78.
When mode selector 52 indicates selection of the on-demand
four-wheel drive mode, ECU 58 energizes motor 156 for initially
rotating cam 178 until pressure plate 140 is located in an
intermediate or "ready" position which, in turn, results in
ballramp unit 80 moving first cam member 110 from its released
position to a "stand-by" position. Accordingly, a predetermined
minimum amount of drive torque is delivered to front output shaft
42 through transfer clutch 50 in this adapt-ready condition.
Thereafter, ECU 58 determines when and how much drive torque needs
to be transferred to front output shaft 42 based on the current
tractive conditions and/or operating characteristics of the motor
vehicle, as detected by sensors 54. Sensors 54 detect such
parameters as, for example, the rotary speed of the output shafts,
the vehicle speed and/or acceleration, the transmission gear, the
on/off status of the brakes, the steering angle, the road
conditions, etc. Such sensor signals are used by ECU 58 to
determine a desired output torque value utilizing a control scheme
that is incorporated into ECU 58. This desired torque value is used
to actively control actuation of electric motor 156 to generate a
rotated position of rotary cam 178.
In addition to adaptive torque control, the present invention
permits release of transfer clutch 50 in the event of an ABS
braking condition or during the occurrence of an over-temperature
condition. Furthermore, while the control scheme was described
based on an on-demand strategy, it is contemplated that a
differential or "mimic" control strategy could likewise be used.
Specifically, the torque distribution between rear output shaft 32
and front output shaft 42 can be controlled to maintain a
predetermined rear/front ratio (i.e., 70:30, 50:50, etc.) so as to
simulate the inter-axle torque splitting feature typically provided
by a mechanical differential unit. Regardless of the control
strategy used, accurate control of the angular position of rotary
cam 178 will result in the desired torque transfer characteristics
across transfer clutch 50. Furthermore, it should be understood
that mode select mechanism 56 could also be arranged to permit
selection of only two different drive modes, namely the on-demand
4WD mode and the part-time 4WD mode. Alternatively, mode select
mechanism 56 could be eliminated such that the on-demand 4WD mode
is always operating in a manner that is transparent to the vehicle
operator.
To illustrate an alternative power transmission device to which the
present invention is applicable, FIG. 5 schematically depicts a
front-wheel based four-wheel drivetrain layout 10' for a motor
vehicle. In particular, engine 18 drives a multi-speed transmission
20' having an integrated front differential unit 38' for driving
front wheels 34 via axle shafts 33. A transfer unit or power
take-off unit (PTU) 300 is also driven by transmission 20' for
delivering drive torque to the input member of a torque transfer
mechanism, such as an in-line torque transfer coupling 302, via a
drive shaft 30'. Torque transfer coupling 302 is preferably
integrated with the components of conventional axle assembly 26 to
define a drive axle assembly 26'. In particular, the input member
of torque coupling 302 is coupled to drive shaft 30' while its
output member is coupled to a drive component of rear differential
28 which, in turn, drives rear wheels 24 via axleshafts 25.
Accordingly, when sensors 54 indicate the occurrence of a front
wheel slip condition, ECU 58 adaptively controls actuation of
torque coupling 302 such that drive torque is delivered "on-demand"
to rear wheels 24. It is contemplated that torque transfer coupling
302 includes a transfer clutch and an electromechanical clutch
actuator that are similar in both structure and function to the
torque transfer mechanism previously described herein. Accordingly,
common reference numerals will be used hereinafter to identify
components previously described.
Referring to FIG. 6, torque coupling 302 is schematically
illustrated to be operably disposed between drive shaft 30' and
rear differential 28. Rear differential 28 includes a pair of side
gears 304 that are connected to rear wheels 24 via rear axle shafts
25. Differential 28 also includes pinions 306 that are rotatably
supported on pinion shafts fixed to a carrier 308 and which mesh
with side gears 304. A right-angled drive mechanism is associated
with differential 28 and includes a ring gear 310 that is fixed for
rotation with carrier 308 and meshed with a pinion gear 312 that is
fixed for rotation with a pinion shaft 314. Torque coupling 302 is
schematically shown to include various components of transfer
clutch 50 that are operably disposed between drive shaft 30' and
pinion shaft 314. In particular, transfer clutch 50 is
schematically shown to include main friction clutch 78 and ballramp
unit 80 as well as pilot friction clutch 82 and thrust bearing unit
84. Torque coupling 302 also is shown schematically to include
clutch actuator 52 that can be adaptively actuated for controlling
the magnitude of the clutch engagement force applied to transfer
clutch 50 and thus the amount of drive torque transferred from
drive shaft 30' to rear differential 28. Actuator 52 includes
clutch operator 152 and power unit 154 previously disclosed in FIG.
4 for adaptively controlling actuation of transfer clutch 50. In
this regard, power transfer system 44 is hereinafter illustrated in
block format and is contemplated to include all electrical and
mechanical components and sub-systems required to adaptively
control actuation of transfer clutch 50.
Torque coupling 302 permits operation in any of the drive modes
previously disclosed. For example, if the on-demand 4WD mode is
selected, ECU 58 regulates activation of clutch actuator 52 in
response to the operating conditions detected by sensors 54 by
controllably varying the electric control signal sent motor 156.
Selection of the part-time 4WD mode results in complete engagement
of main clutch pack 90 such that pinion shaft 314 is, in effect,
rigidly coupled to driveshaft 30'. Finally, in the two-wheel drive
mode, main clutch pack 90 is released such that pinion shaft 312 is
free to rotate relative to driveshaft 30'. Alternatively,
elimination of mode select mechanism 56 would provide automatic
adaptive operation of torque coupling 302.
The arrangement shown for drive axle assembly 26' of FIG. 6 is
operable to provide on-demand four-wheel drive by adaptively
controlling the transfer of drive torque from the primary driveline
to the secondary driveline. In contrast, a drive axle assembly 320
is shown in FIG. 7 wherein torque coupling 302 is now operably
installed between differential case 308 and one of axleshafts 25 to
provide an adaptive "side-to-side" torque biasing and slip limiting
feature. Torque coupling 302 is schematically shown to again
include transfer clutch 50 and clutch actuator 52, the construction
and function of which are understood to be similar to the detailed
description previously provided herein for each sub-assembly.
Referring now to FIG. 8, a drive axle assembly 322 is schematically
shown to include a pair of torque couplings 302L and 302R that are
operably installed between a driven pinion shaft 314 or 30' and
axleshafts 25. The driven pinion shaft drives a right-angled
gearset including pinion 312 and ring gear 310 which, in turn,
drives a transfer shaft 324. First torque coupling 302L is shown
disposed between transfer shaft 324 and the left one of axleshafts
25 while second torque coupling 302R is disposed between transfer
shaft 324 and the right axle shaft 25. Each torque coupling
includes a corresponding transfer clutch 50L, 50R and clutch
actuator 52L, 52R. Accordingly, independent torque transfer and
slip control is provided between the driven pinion shaft and each
rear wheel 24 pursuant to this arrangement.
To illustrate additional alternative power transmission devices to
which the present invention is applicable, FIG. 9 schematically
depicts a front-wheel based four-wheel drive drivetrain layout 10''
for a motor vehicle. In particular, engine 18 drives multi-speed
transaxle 20' which has an integrated front differential unit 38'
for driving front wheels 34 via axle shafts 33. As before, PTU 300
is also driven by transaxle 20' for delivering drive torque to the
input member of a torque transfer coupling 330. The output member
of torque transfer coupling 330 is coupled to propshaft 30' which,
in turn, drives rear wheels 24 via axleshafts 25. Rear axle
assembly 26 can be a traditional driven axle with a differential
or, in the alternative, be similar to the drive axle arrangements
described in regard to FIGS. 7 or 8. Accordingly, in response to
detection of certain vehicle characteristics by sensors 54 (i.e.,
the occurrence of a front wheel slip condition), power transfer
system 44 causes torque coupling 330 to deliver drive torque
"on-demand" to rear wheels 24. It is contemplated that torque
coupling 330 would be generally similar in structure and function
to that of torque transfer coupling 302 previously described
herein. As such, its primary components of transfer clutch 50 and
clutch actuator 52 are again schematically shown.
Referring now to FIG. 10, torque coupling 330 is schematically
illustrated in association with an on-demand four-wheel drive
system based on a front-wheel drive vehicle similar to that shown
in FIG. 9. In particular, an output shaft 332 of transaxle 20' is
shown to drive an output gear 334 which, in turn, drives an input
gear 336 that is fixed to a carrier 338 associated with front
differential unit 38'. To provide drive torque to front wheels 34,
front differential unit 38' includes a pair of side gears 340 that
are connected to front wheels 34 via axleshafts 33. Differential
unit 38' also includes pinions 342 that are rotatably supported on
pinion shafts fixed to carrier 338 and which are meshed with side
gears 340. A transfer shaft 344 is provided for transferring drive
torque from carrier 338 to a clutch hub 84 associated with transfer
clutch 50. PTU 300 is a right-angled drive mechanism including a
ring gear 346 fixed for rotation with drum 88 of transfer clutch 50
and which is meshed with a pinion gear 348 fixed for rotation with
propshaft 30'. According to the present invention, the components
schematically shown for torque transfer coupling 330 are understood
to be similar to those previously described. In operation, drive
torque is adaptively transferred on-demand from the primary (i.e.,
front) driveline to the secondary (i.e., rear) driveline.
Referring to FIG. 11, a modified version of the power transmission
device shown in FIG. 10 is now shown to include a second torque
coupling 330A that is arranged to provide a limited slip feature in
association with primary differential 38'. As before, adaptive
control of torque coupling 330 provides on-demand transfer of drive
torque from the primary driveline to the secondary driveline. In
addition, adaptive control of second torque coupling 330A provides
on-demand torque biasing (side-to-side) between axleshafts 33 of
primary driveline 14. As seen, common components of torque coupling
330A are identified with an "A" suffix.
FIG. 12 illustrates another modified version of FIG. 9 wherein an
on-demand four-wheel drive system is shown based on a rear-wheel
drive motor vehicle that is arranged to normally deliver drive
torque to rear wheels 24 while selectively transmitting drive
torque to front wheels 34 through a torque coupling 330. In this
arrangement, drive torque is transmitted directly from transmission
output shaft 332 to power transfer unit 300 via a drive shaft 350
which interconnects input gear 336 to ring gear 346. To provide
drive torque to front wheels 34, torque coupling 330 is shown
operably disposed between drive shaft 350 and transfer shaft 344.
In particular, transfer clutch 50 is arranged such that drum 88 is
driven with ring gear 346 by drive shaft 350. As such, clutch
actuator 52 functions to transfer drive torque from drum 88 through
clutch pack 90 to hub 84 which, in turn, drives carrier 338 of
differential unit 38' via transfer shaft 344.
In addition to the on-demand four-wheel drive systems shown
previously, the power transmission technology of the present
invention can likewise be used in full-time four-wheel drive
systems to adaptively bias the torque distribution transmitted by a
center or "interaxle" differential unit to the front and rear
drivelines. For example, FIG. 13 schematically illustrates a
full-time four-wheel drive system which is generally similar to the
on-demand four-wheel drive system shown in FIG. 12 with the
exception that an interaxle differential unit 360 is now operably
installed between carrier 338 of front differential unit 38' and
transfer shaft 344. In particular, output gear 336 is fixed for
rotation with a carrier 362 of interaxle differential 360 from
which pinion gears 364 are rotatably supported. A first side gear
366 is meshed with pinion gears 364 and is fixed for rotation with
drive shaft 350 so as to be drivingly interconnected to the rear
driveline through power transfer unit 300. Likewise, a second side
gear 368 is meshed with pinion gears 364 and is fixed for rotation
with carrier 338 of front differential unit 38' so as to be
drivingly interconnected to the front driveline. Torque coupling
330 is now shown to be operably disposed between side gears 366 and
368. Torque coupling 330 is operably arranged between the driven
outputs of interaxle differential 360 for providing an adaptive
torque biasing and slip limiting function between the front and
rear drivelines.
Referring now to FIG. 14, a full-time 4WD system is shown to
include a transfer case 22' which is generally similar to transfer
case 22 of FIG. 2 except that an interaxle differential 380 is
provided between an input shaft 382 and output shafts 32 and 42. As
is conventional, input shaft 382 is driven by the output of
transmission 20. Differential 380 includes an input defined as a
planet carrier 384, a first output defined as a first sun gear 386,
a second output defined as a second sun gear 388, and a gearset for
permitting speed differentiation between first and second sun gears
386 and 388. The gearset includes a plurality of meshed pairs of
first planet gears 390 and second pinions 392 which are rotatably
supported by carrier 384. First planet gears 390 are shown to mesh
with first sun gear 386 while second planet gears 392 are meshed
with second sun gear 388. First sun gear 386 is fixed for rotation
with rear output shaft 32 so as to transmit drive torque to the
rear driveline. To transmit drive torque to the front driveline,
second sun gear 388 is coupled to transfer assembly 96 which again
includes first sprocket 98 rotatably supported on rear output shaft
32, second sprocket 100 fixed to front output shaft 42, and power
chain 102.
A number of preferred embodiments have been disclosed to provide
those skilled in the art an understanding of the best mode
currently contemplated for the operation and construction of the
present invention. The invention being thus described, it will be
obvious that various modifications can be made without departing
from the true spirit and scope of the invention, and all such
modifications as would be considered by those skilled in the art
are intended to be included within the scope of the following
claims.
* * * * *